Oxynitridation is an attractive way for scaling down tunnel oxide during the production of non-volatile memory devices. However, during the oxynitridation process, contaminate nitrogen incorporates into the peripheral transistor gate oxide layer and forms an Si--N bond with the surface of the silicon substrate in contact with the gate oxide layer. This contaminate nitrogen can not be effectively removed using conventional hydrofluoric acid dip or reoxidation techniques. The presence of such contaminate nitrogen contributes to a nonuniform gate oxide growth during subsequent gate oxidation processing. This degrades the peripheral transistor characteristics and makes oxynitridation less attractive for producing non-volatile memory devices. The present invention provides an effective way for removing this contaminate nitrogen and thus provides a solution for growing high quality gate oxide as well as taking advantage of the use of oxynitridation for tunnel oxide.